Influence of Surface Roughening of Rutile Single-Crystalline TiO2 on Photocatalytic Activity for Oxygen Photoevolution from Water in Acidic and Alkaline Solutions

We previously found that a TiO 2 surface was atomically roughened with the progress of the photo-oxidation reaction of water. Considering the fact that surface local structures affect the photocatalytic activity, the activity may be changed by the surface roughening. In this paper, the photocatalytic activities for oxygen evolution of the roughened and atomically flat TiO 2 single-crystal electrodes in acidic and alkaline solutions were investigated. In the low pH (acidic condition) aqueous solution, the onset potential of the roughened TiO 2 for oxygen photoevolution was shifted toward the negative side by 0.20–0.15 V from that of the atomically flat TiO 2, whereas the shifts of the flat-band potential between them were much smaller than that of the onset potential. This result indicated that the activation energy for oxygen photoevolution of the roughened TiO 2 was lower than that of the atomically flat TiO 2 . On the other hand, in the high pH (alkaline condition) aqueous solution, the onset potentials of both roughened and flat TiO 2 were almost the same. This result implies that the oxygen photoevolution mechanism at the TiO 2 surface in the alkaline solution was different from that in the acidic solution.